1. Field of the Invention
This invention relates generally to gaskets for making joints fluid-tight, and more particularly to a composite material suitable for making gaskets in any desired configuration, the composite material being composed of a perforated metal sheet having tangs struck out therefrom sandwiched between facing layers having sealing properties and compression laminated thereto.
2. Status of Prior Art
A gasket is a packing used to prevent leakage of fluid through mechanical joints. Gaskets are commonly installed in static clearances between parallel flanges, sealing being effected by compressive loading by means of bolts. Gaskets come in a variety of forms, such as simple ring gaskets made of rubber, a rubberized asbestos cloth, or a corrugated sheet with a filling in the corrugations.
The concern of the present invention is with gaskets which are formed of a composite material composed of a metal core and facing layers having sealing properties laminated thereto, the composite being die cut or otherwise shaped to define a gasket of the desired configuration. One such composite material is disclosed in the Victor U.S. Pat. No. 1,897,088, in which a metal core sheet having triangular prongs struck out of the sheet on opposing sides thereof is sandwiched between facing layers of asbestos material. The sandwich is first fed between soft compression rolls which cause the prongs to pierce through and stick out of the asbestos layers. Then the sandwich is fed between hard compression rolls which act to bend over the points of the prongs to cause them to clinch the asbestos layers.
In the Victor arrangement, each punched hole in the metal core has a triangular form, the punching action creating for each hole a single straight triangular tang. As a consequence, the holding power of the tangs is limited.
A similar gasket composite is disclosed in the Balfe U.S. Pat. No. 1,927,450, in which a metal core having straight triangular prongs or tangs struck out from the holes, one for each hole, project from the opposite sides of the metal core, the tangs penetrating packing layers and being clinched over these layers.
In the gasketing material shown in the Niessen et al. U.S. Pat. No. 2,992,151, the core is a sheet of metal that has been expanded laterally to produce closely-spaced projections rising out of each side of the core sheet, the core sheet being compressed between layers of elastomeric material whereby the projections from the core sheet penetrate these layers.
In Nakamura et al., 4,591,170, the metal core sheet of the composite gasketing material is so punched as to create tangs each having three points thereon. These multi-pointed tangs penetrate facing layers of heat-resistent sealing material, such as asbestos or graphite. The Yamazoe et al. U.S. Pat. No. 4,234,638 also discloses a composite material for gaskets in which prongs projecting from opposite sides of a core sheet penetrate graphite facing layers.
In the Gallo U.S. Pat. No. 4,776,602 and the Gallo et al. U.S. Pat. No. 4,822,062, the gasket is formed from a perforated metal core sheet joined to facing layers. The retaining means for this purpose are formed by a pair of opposed tangs on opposite sides of each perforation in the core sheet.
Gaskets have innumerable applications, for they are used in automobile and other engines, in chemical and industrial apparatus, nuclear reactors, and in various mechanisms where the gaskets may be subjected to elevated temperatures and highly reactive chemical fluids.
Thus desirable in such applications as the sealing or packing layers of a gasket is Kevlar, this being the trademark for an aromatic polyamide fiber of extremely high tensile strength whose resistance to elongation is greater even than steel. Kevlar is usable as a reinforcing material for plastic composite. Also usable as a sealing layer is Teflon, which is the trademark for tetrafluoroethylene, a fluorocarbon which is available in fibrous or in sheet form.
Some high-strength cellulosic materials are also usable as packing layers. But whether the layers are of Kevlar, Teflon, graphite, or of a cellulosic composition, it is essential that these layers be securely laminated to the metal core sheet, and that no chemical bonding agent be used for this purpose, for such agents may be attacked by highly reactive fluids.
When a composite for a gasket is composed of Kevlar layers compression-laminated to opposite sides of a perforating metal core sheet whose sharp prongs or tangs pierce the Kevlar layers, then it is not only important that the tangs function to securely lock the layers to the core sheet to prevent delamination of the composite material, but also that the tangs be embedded within the Kevlar layers and not go through the outer surfaces of these layers. Should the points of the tangs which pierce the Kevlar layers extend beyond the outer surface of the Kevlar layers, the integrity of the Kevlar as a chemically resistant sealing barrier would be impaired.